[mod_python] mod_python or apache scalability?

> Are you using Sessions, specifically DbmSession?
> 
> Jim

We are not using DbmSession

Alec

> -----Original Message-----
> From: Jim Gallacher [mailto:jpg at jgassociates.ca]
> Sent: Monday, October 01, 2007 4:55 AM
> To: Alec Matusis
> Cc: mod_python at modpython.org
> Subject: Re: [mod_python] mod_python or apache scalability?
> 
> Are you using Sessions, specifically DbmSession?
> 
> Jim
> 
> 
> Alec Matusis wrote:
> > I am sorry in advance if this turns out to be an apache-related
> issue, but
> > when I posted this on apache list, it has been suggested that it
> might be an
> > application issue, so I am reposting it here.
> >
> >
> > We are running a busy mod_python/3.1.4 Python/2.4.1 server on 2.6.9
> kernel,
> > that suddenly becomes very slow- requests either time out, or it
> takes
> > 10-20sec to serve a 1K thumbnail.
> > It is somewhat correlated with load spikes, but not perfectly (by
> looking at
> > the bandwidth graph, it never happens during the low bandwidth
> periods at
> > night, but it does not coincide with peaks of b/w)
> >
> > When we initially encountered an apache overload, it was always
> accompanied
> > with
> >
> > [error] server reached MaxClients setting, consider raising the
> MaxClients
> > setting
> >
> > in the apache error log. We also got
> >
> > kernel: possible SYN flooding on port 80. Sending cookies.
> >
> > in /var/log/messages system log.
> >
> > After that I raised MaxClients from 200 to 300. The problem initially
> > disappeared, but after our bandwidth grew a bit more, we got this
> behavior
> > again.
> > Now apache crashes (becomes very slow) silently, with no warning in
> apache
> > error logs at all (although we still get SYN flood message in the
> system
> > log)
> > When apache is this 'slow' regime, /server-status still shows
> available
> > slots, i.e. MaxClients is not reached.
> >
> > This is the relevant part of httpd.conf:
> >
> > ServerLimit 300
> > # we are using prefork MPM
> > StartServers 10
> > MinSpareServers 5
> > MaxSpareServers 20
> > MaxClients 300
> > MaxRequestsPerChild 10000
> > MaxMemFree 2500
> >
> > The server has 4GB of physical RAM and 4GB of swap. During these
> apache
> > "slowdowns", the swap size is still 0 and vmstat shows no swapping at
> all.
> > I suspect the problem may be in
> >
> > MaxMemFree 2500
> >
> > but then I would expect some kind of  "out of memory" errors in the
> logs?
> >
> > I am posting it on this list since I have not gotten a response in
> the users
> > list, and I think it's a bug for two reasons:
> >
> > 1) When apache is in this slow "degraded" regime, I would expect a
> log
> > message in the apache error log, with an explanation why.
> >
> > 3) If this is related to resource exhaustion, I would expect the
> server to
> > recover from this regime by itself when the load subsides, but this
> is not
> > the case. Only apachectl start/stop recovers the server.
> >
> >
> >
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> >